Technical Field
The present disclosure relates to fluidizable vanadium based VOx—Nb/La—Al2O3 catalysts for the oxidative dehydrogenation of alkanes in the absence of gas phase oxygen.
Description of the Related Art
The “background” description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description which may not otherwise qualify as prior art at the time of filing, are neither expressly or impliedly admitted as prior art against the present invention.
Ethylene is a starting material for several industrial syntheses. It is used as an important intermediate in the chemical industry, as well as to produce polyethylene [S. A. R. Mulla, O. V. Buyevskaya, and M. Baerns, “A comparative study on non-catalytic and catalytic oxidative dehydrogenation of ethane to ethylene,” vol. 226, pp. 73-78, 2002.]. Conventionally, ethylene is produced by cracking processes (mainly steam cracking). However, these processes require high energy consumption, which contributes to a high production cost. Alternatively, catalytic oxidative dehydrogenation (ODH) is an emerging technology which can eliminate some of the drawbacks associated with conventional cracking processes. Since oxidative dehydrogenation catalysts play an important role in such reactions, much ongoing research work focuses on different aspects of the catalysis. These aspects include catalyst active phases, structure and morphology which all are responsible for catalyst performance. Furthermore, in the area of oxidative dehydrogenation of ethane catalyst selectivity can be one of the most important factors effecting performance, in addition to catalyst stability and other parameters.
Supported metal oxides are common catalysts for oxidative dehydrogenation reactions, and modifying the catalyst support is an effective way to enhance performance. It has been established that the support can have a major effect on catalyst performance. For instance, vanadium (V) and chromium (Cr) oxides on different supports have been tested [M. Loukah, J. C. Vedrine, and M. Ziyad, “Oxidative dehydrogenation of ethane on V- and Cr-based phosphate catalysts,” vol. 4, 1995.]. It was reported that at an equivalent conversion extent, ethylene selectivity followed the order of VO2P2O7>CrPO4>Cr/α-ZrP>Cr/β-ZrP. In addition, TiO2 supported VOPO4 catalysts have shown good selectivity in the oxidative dehydrogenation of ethane demonstrating higher ethylene productivity than that reported for (VO)2P2O7 [P. Ciambelli, P. Galli, L. Lisi, M. A. Massucci, P. Patrono, R. Pirone, G. Ruoppolo, and G. Russo, “TiO 2 supported vanadyl phosphate as catalyst for oxidative dehydrogenation of ethane to ethylene,” vol. 203, pp. 133-142, 2000.—incorporated herein by reference in its entirety]. Furthermore, iron phosphate phases have also been considered, such as FePO4, Fe2P2O7, α-Fe3(P2O7) and β-Fe3(P2O7) [J. E. Miller, M. M. Gonzales, L. Evans, A. G. Sault, C. Zhang, R. Rao, G. Whitwell, A. Maiti, and D. King-Smith, “Oxidative dehydrogenation of ethane over iron phosphate catalysts,” Appl. Catal. A Gen., vol. 231, no. 1-2, pp. 281-292, May 2002.—incorporated herein by reference in its entirety]. Nickel (Ni) and Ni—Co/Al2O3 powder catalysts have also been investigated and were found active and selective for this reaction but with lower conversion and less selectivity (less than 30%) [J. P. Bortolozzi, L. B. Gutierrez, and M. a. Ulla, “Synthesis of Ni/Al2O3 and Ni—Co/Al2O3 coatings onto AISI 314 foams and their catalytic application for the oxidative dehydrogenation of ethane,” Appl. Catal. A Gen., vol. 452, pp. 179-188, February 2013.—incorporated herein by reference in its entirety].
Catalysts such as AlPO-34, SAPO-34, NaAPSO-34 and LaAPSO-34 were also studied for oxidative dehydrogenation, and it was observed that cracking reactions are inhibited on SAPO-34 catalysts where deactivation effects were practically absent even after a 12 hour experiment. When metals such as vanadium (V), cobalt (Co), magnesium (Mg) or manganese (Mn) are introduced to the ALPO-5 structure good activity is obtained at temperatures of 425-600° C. However, ethylene selectivity did not exceed 65% at 7.5% ethane conversion, and the contact time used was greater than that used for the SAPO-34 based catalysts [L. Marchese, “Acid SAPO-34 Catalysts for Oxidative Dehydrogenation of Ethane,” J. Catal., vol. 208, no. 2, pp. 479-484, June 2002.]. Vanadium with titanium (Ti), tin (Sn) or zirconium (Zr) pyrophophates support were also studied in the oxidative dehydrogenation reaction, and exhibited a good conversion (20%) and selectivity (over 90%) at 560° C. Notably, this performance is again related to vanadium (V) as a surface species [L. Lisi, G. Ruoppolo, M. P. Casaletto, P. Galli, M. a. Massucci, P. Patrono, and F. Pinzari, “Vanadium-metal(IV)phosphates as catalysts for the oxidative dehydrogenation of ethane,” J. Mol. Catal. A Chem., vol. 232, no. 1-2, pp. 127-134, May 2005.—incorporated herein by reference in its entirety].
Another way to improve catalyst performance is the addition of promoters. Metal promoters isolate active species and can form secondary metal oxides on support surfaces. For example, molybdenum (Mo) based catalysts were examined with the addition of vanadium and phosphorous. It was observed that vanadium and phosphorous increase catalyst efficiency [N. Haddad, E. Bordes-Richard, L. Hilaire, and a. Barama, “Oxidative dehydrogenation of ethane to ethene on alumina-supported molybdenum-based catalysts modified by vanadium and phosphorus,” Catal. Today, vol. 126, no. 1-2, pp. 256-263, August 2007.—incorporated herein by reference in its entirety]. Chromium (Cr) containing oxide pillared zirconium phosphate was synthesized using the fluoro-complex method, and the catalyst was found to be active in oxidative dehydrogenation reactions due to the presence of Cr oxide [B. Solsona, J. M. López-Nieto, M. Alcántara-Rodríguez, E. Rodríguez-Castellón, and a. Jiménez-López, “Oxidative dehydrogenation of ethane on Cr, mixed Al/Cr and mixed Ga/Cr oxide pillared zirconium phosphate materials,” J. Mol. Catal. A Chem., vol. 153, no. 1-2, pp. 199-207, March 2000.—incorporated herein by reference in its entirety]. A novel catalyst of BaCl2—TiO2—SnO2 has also been developed [Z. Wang, L. Chen, G. Zou, X. Luo, R. Gao, L. Chou, and X. Wang, “A novel BaCl2—TiO2—SnO2 catalyst for the oxidative dehydrogenation of ethane,” Catal. Commun., vol. 25, no. 3, pp. 45-49, August 2012.—incorporated herein by reference in its entirety], and interestingly this catalyst at 720° C. gave very high selectivity for ethylene, and most importantly the COx selectivity was very low (7%). For this catalyst, Cl− ions in the catalyst play a vital and positive role in the oxidative dehydrogenation reaction. Although the catalyst BaCl2—TiO2—SnO2 has deactivation difficulties, the promising result of 60.4% ethylene yield and 92.6% ethylene selectivity made it a promising alternative for ethylene synthesis using a low cost feedstock such as ethane. Lanthanum (La), neodymium (Nd), samarium (Sm) and gadolinium (Gd) based catalysts have been synthesized by modified Sol-gel methods [Q. Zhou, D. Zhou, Y. Wu, and T. Wu, “Oxidative dehydrogenation of ethane over RE-NiO (RE=La, Nd, Sm, Gd) catalysts,” J. Rare Earths, vol. 31, no. 7, pp. 669-673, July 2013.—incorporated herein by reference in its entirety]. Gd—NiO showed the best catalytic performance for oxidative dehydrogenation reactions, with 56% ethane conversion and 51% ethylene selectivity at 375° C. Cobalt-titania catalysts were also investigated with the addition of phosphorous [Y. Brik, “Titania-Supported Cobalt and Cobalt-Phosphorus Catalysts: Characterization and Performances in Ethane Oxidative Dehydrogenation,” J. Catal., vol. 202, no. 1, pp. 118-128, August 2001.—incorporated herein by reference in its entirety]. The activity of cobalt-titania (anatase) catalysts in oxidative dehydrogenation of ethane was maximal when 7.6 wt % of cobalt was added.
Y-zeolites were treated with transition metals (Ni, Cu and Fe) and then employed in the oxidative dehydrogenation reaction [X. Lin, C. a. Hoel, W. M. H. Sachtler, K. R. Poeppelmeier, and E. Weitz, “Oxidative dehydrogenation (ODH) of ethane with O2 as oxidant on selected transition metal-loaded zeolites,” J. Catal., vol. 265, no. 1, pp. 54-62, July 2009.—incorporated herein by reference in its entirety]. It was reported that catalyst activity and C2H4 selectivity depend on the active metal and follows the trend of Ni>Cu>Fe. In addition, when these metals were used without support, it is reported that they gave selectivity in the range of 50% to 60% at 600 K [Y. Schuurman, V. Ducarme, T. Chen, W. Li, C. Mirodatos, and G. A. Martin, “Low temperature oxidative dehydrogenation of ethane over catalysts based on group VIII metals,” Appl. Catal. A Gen., vol. 163, no. 1-2, pp. 227-235, December 1997.—incorporated herein by reference in its entirety].
Lithium (Li), magnesium (Mg), aluminum (Al), gallium (Ga), titanium (Ti), niobium (Nb), and tantalum (Ta) have also been used to enhance the properties of Ni-based mixed metal oxides [Y. Wu, J. Gao, Y. He, and T. Wu, “Preparation and characterization of Ni—Zr—O nanoparticles and its catalytic behavior for ethane oxidative dehydrogenation,” Appl. Surf. Sci., vol. 258, no. 11, pp. 4922-4928, March 2012.—incorporated herein by reference in its entirety]. Furthermore, NiO and Nb—NiO nanocomposites have been prepared based on the slow oxidation of a nickel riche Nb—Ni gel obtained in citric acid [H. Zhu, S. Ould-Chikh, D. H. Anjum, M. Sun, G. Biausque, J.-M. Basset, and V. Caps, “Nb effect in the nickel oxide-catalyzed low-temperature oxidative dehydrogenation of ethane,” J. Catal., vol. 285, no. 1, pp. 292-303, January 2012.—incorporated herein by reference in its entirety]. The resulting materials have higher surface areas than those obtained by those obtained by the classical evaporation method from nickel nitrate and ammonium niobium oxalate.
Additional work has also been done on nanosized catalysts, specifically a Ni—Zr—O mixture which is prepared by a sol-gel method. Vanadium and phosphorous have also been considered as promoters to enhance the performance in terms of conversion stability and selectivity, but it was found to be less effective than in the molybdenum (Mo) based catalyst [N. Haddad, E. Bordes-Richard, and a. Barama, “MoOx-based catalysts for the oxidative dehydrogenation (ODH) of ethane to ethylene,” Catal. Today, vol. 142, no. 3-4, pp. 215-219, April 2009.—incorporated herein by reference in its entirety]. V2O5/Nb2O5 catalysts with various N2O5 contents were also studied [A. Qiao, V. N. Kalevaru, J. Radnik, a. Srihari Kumar, N. Lingaiah, P. S. Sai Prasad, and a. Martin, “Oxidative dehydrogenation of ethane to ethylene over V2O5/Nb2O5 catalysts,” Catal. Commun., vol. 30, pp. 45-50, January 2013.—incorporated herein by reference in its entirety]. The ethylene sensitivity obtained is 38% with a corresponding 28% yield. The activity of the catalyst was related to vanadium (V) species formed, but the low activity presented was attributed to the very low yield of pure Nb2O5, which is 4%. MoO3—V2O5/Al2O3 is also an effective catalyst in ethane dehydrogenation; however, molybdenum (Mo) addition in this case enhanced catalyst performance by the formation of Mo—V mixed oxides [A. Sri Hari Kumar, K. Upendar, a. Qiao, P. S. N. Rao, N. Lingaiah, V. N. Kalevaru, a. Martin, C. Sailu, and P. S. Sai Prasad, “Selective oxidative dehydrogenation of ethane over MoO3/V2O5-Al2O3 catalysts: Heteropolymolybdate as a precursor for MoO3,” Catal. Commun., vol. 33, pp. 76-79, 2013.—incorporated herein by reference in its entirety]. MoVTeNbO was also tested for ethane oxidative dehydrogenation, with the catalyst prepared using a slurry method which was started by silica addition. It was reported that the addition of silica and the synthesis method improved catalyst structure and ultimately the efficiency [T. T. Nguyen, L. Burel, D. L. Nguyen, C. Pham-Huu, and J. M. M. Millet, “Catalytic performance of MoVTeNbO catalyst supported on SiC foam in oxidative dehydrogenation of ethane and ammoxidation of propane,” Appl. Catal. A Gen., vol. 433-434, pp. 41-48, 2012.—incorporated herein by reference in its entirety]. The synthesis method also had a great effect on catalyst structure and performance. It was reported that MoVNbTeOx catalyst gave good results after it was post treated with oxalic acid, which improved the catalyst surface area, and therefor catalyst selectivity and conversion were increased up to 85% and 73% respectively [B. Chu, L. Truter, T. A. Nijhuis, and Y. Cheng, “Applied Catalysis A: General Performance of phase-pure M1 MoVNbTeOx catalysts by hydrothermal synthesis with different post-treatments for the oxidative dehydrogenation of ethane,” “Applied Catal. A, Gen., vol. 498, pp. 99-106, 2015.—incorporated herein by reference in its entirety].
Reactor type can also affect the oxidative dehydrogenation reaction and different reactor types such as a fluidized bed membrane reactor and a multi-tubular fixed-bed reactor have been utilized for oxidative dehydrogenation [D. Ahchieva, M. Peglow, S. Heinrich, L. Mörl, T. Wolff, and F. Klose, “Oxidative dehydrogenation of ethane in a fluidized bed membrane reactor,” Appl. Catal. A Gen., vol. 296, no. 2, pp. 176-185, December 2005; and E. López, E. Heracleous, A. a. Lemonidou, and D. O. Borio, “Study of a multitubular fixed-bed reactor for ethylene production via ethane oxidative dehydrogenation,” Chem. Eng. J., vol. 145, no. 2, pp. 308-315, December 2008.—each incorporated herein by reference in its entirety]. However, only a few studies have reported good ethylene selectivity using these reactors. Furthermore, in the majority of literature, oxygen (O2) was introduced as a gas phase reactant, which can increase feed combustion and lower ethylene selectivity.
An oxygen free environment has been employed to study the ethane oxidative dehydrogenation reaction in fluidized bed reactor conditions (FIG. 1) using 10% VOx supported on c-Al2O3[S. Al-Ghamdi, M. Volpe, M. M. Hossain, and H. de Lasa, “VOx/c-Al2O3 catalyst for oxidative dehydrogenation of ethane to ethylene: Desorption kinetics and catalytic activity,” Appl. Catal. A Gen., vol. 450, pp. 120-130, January 2013.—incorporated herein by reference in its entirety]. Reactivity tests showed that the prepared oxidative dehydrogenation catalyst displayed 6.5-27.6% ethane conversion and 57.6-84.5% ethylene selectivity in the 550-600° C. range. Moderate metal-support interaction and good VOx dispersion was credited as the key to achieving this desired catalytic performance. In another study, molybdenum (Mo) was introduced to a VOx/Al2O3 catalyst, which further enhanced catalyst performance by the formation of MoOx as secondary surface oxides [I. A. Bakare, S. A. Mohamed, S. Al-Ghamdi, S. A. Razzak, M. M. Hossain, and H. I. de Lasa, “Fluidized bed ODH of ethane to ethylene over VOx-MoOx/γ-Al2O3 catalyst: Desorption kinetics and catalytic activity,” Chem. Eng. J., 2014.—incorporated herein by reference in its entirety].
In view of the forgoing, one object of the present disclosure is to provide novel dehydrogenation catalysts comprising a VOx catalyst with niobium (Nb) as a promoter to improve VOx isolation on a support surface of alumina (Al2O3) modified with lanthanum (La) to minimize the possibility of high temperature alumina phase transition and to afford better thermal stability of the catalyst. A further aim of the present disclosure is to provide a method for producing these multicomponent VOx—Nb/La—Al2O3 catalysts. An additional aim of the present disclosure is to provide a method for the oxidative dehydrogenation of an alkane to a corresponding olefin employing these multicomponent VOx—Nb/La—Al2O3 catalysts that may be performed in a gas phase oxygen free environment under circulating fluidized bed reaction conditions while enhancing alkane conversion and alkene selectivity.